Visco-Elastic Honeycomb Structures with Increased Energy Absorption and Shape Recovery Performance Using Buckling Initiators.

Energy-absorbing materials have extensive applications in aerospace and automotive applications. Research has shown buckling initiators, or triggers, in energy-absorbing tubular structures increase the energy absorbed by encouraging the side panels to fold when loaded out of plane in compression conditions. Additively manufactured TPE honeycombs were designed in this study to include these buckling initiators, which introduced a slight decrease in initial weight, as well as initial stress concentrations, while improving crashworthiness characteristics. The samples with buckling initiators (1BI) showed an increase in crush efficiency when directly compared to their no buckling initiator (0BI) counterparts. The 1BI samples maintained an increased crush efficiency regardless of the strain rate used. The samples with 1BI were able to better equilibrate the peak stress with the plateau stress. These honeycomb samples were found to maintain their crush efficiency, even after multiple rounds of compression testing. The quasi-static 0BI samples experienced a 23.4% decrease in the peak stress after multiple rounds of compression testing, while the 1BI samples saw approximately a 23.0% decrease. The 1BI samples averaged a decrease in crush efficiency of 0.5%, while the 0BI samples saw a decrease in crush efficiency of 5%. As the strain rate increased, the crush efficiency for the 1BI samples showed an increase in performance, with a smaller degradation in crush efficiency over multiple uses. Visco-elastic honeycomb with buckling initiators has a higher energy absorption than samples with no buckling initiators when exposed to multiple impact cycles.

Hierarchical Composites with Electrophoretically Deposited Carbon Nanotubes for In Situ Sensing of Deformation and Damage.

As composites are used increasingly in structural components, novel techniques for detecting micro-scale damage are required. Their nanoscale size and high aspect ratio allow carbon nanotubes to create electrically conductive pathways that enable sensing. In this work, carbon nanotubes are deposited onto glass fabric using electrophoretic deposition to create hierarchical composites. Polyethylenimine functionalized carbon nanotubes are deposited from an aqueous dispersion using an electric field. Symmetric cross-ply composites are investigated as a model system to demonstrate the ability to detect incipient damage and transverse microcracks. The specimens are subjected to tensile loading, and a resistance increase is observed because of two key mechanisms-a reversible change in nanotube-nanotube tunneling gaps due to elastic straining of the network and a permanent severing of paths in the conducting network due to formation of transverse cracks in the 90° plies. By analyzing the electrical response, the damage state can be identified. Acoustic emission sensors are used to validate the results. The strength and Young's modulus of the composites with integrated carbon nanotubes are similar to the control specimens. Crack density measurements using edge replication reveal that transverse cracking can be suppressed, demonstrating multi-functionality with improved damage tolerance and integrated sensing.

Eyesight: a study of the staff of a dental school.

OBJECTIVES/AIMS: The aim was to investigate the vision of all 90 dentally qualified staff at a dental school. MATERIALS AND METHODS: Ethical approval was obtained and a questionnaire-based survey conducted. Data were screened and analysed using Stata 13.1. The χ2 and Fisher's Exact tests were used to test for significance with an alpha level of 0.05. RESULTS: The participation rate was 95.6%. Most of the teachers (92%) considered their eyesight was satisfactory to practice dentistry. Of the 97% who had been tested at some stage, 15% had their eye examination due to sight deterioration with 22% needing correction. Almost two-thirds were myopic and a third were hyperopic. Forty-nine per cent wore spectacles only, with about a quarter of this group alternating between spectacles and contact lenses. Of those with corrected vision, 80% followed their optometrist's recall advice. Four participants reported that they were colour blind. While 4% had had laser-eye surgery, a further 27% were interested in this. Magnification was used by 72% with no significant differences between genders, age of staff member, place of qualification or registration status. Most of the staff (81%) thought that screening of dental student's eyesight should be mandatory, and regular eye examinations as a condition of dental practice was supported by 67%. DISCUSSION: The number of teachers reporting recent vision tests was encouraging; nevertheless, a worrying 8% surveyed were unsure if their eyesight was satisfactory for work. The commonest vision problem was myopia, with almost half of the teachers wearing spectacles. It is clear that visual standards for dentistry would be helpful. Magnification use was high, with many non-users indicating their intention to buy loupes. CONCLUSIONS: Within the limits of this study the teachers were conscientious regarding their eye care, irrespective of their training and age. There was strong support for the mandatory testing of vision for all dentists and especially dental students.

Undergraduate endodontic teaching in New Zealand: students' experience, perceptions and self-confidence levels.

The aim was to investigate undergraduate students' experiences, perceptions of future practice and self-rated confidence levels across endodontic tasks. After ethical approval, a survey involved all fourth and fifth year students. Quantitative data were analysed in SPSS version 20.0. Qualitative data were analysed using a general inductive approach. The participation rate was 84% (n = 136 of 162). The mean number of canals completed was 2.6 by fourth years and 10.4 by fifth years. Maxillary premolars were the most common first tooth treated. Pulpal factors and root morphology were the most common reasons for experiencing difficulty. Self-rated confidence levels were lower for the more junior students and complex procedures. Students felt that an increased use of extracted natural teeth would be beneficial in their pre-clinical practice. A high level of interest was shown in future specialisation in endodontics. Students may benefit from further didactic teaching or pre-clinical instruction in selected topics.